Prior to the present invention, as shown by Ryang, for Silylnorbornane Anhydrides and Methods for Making, U.S. Pat. No. 4,381,396, assigned to the same assignee as the present invention and incorporated herein by reference, silylnorbornane anhydrides were made by effecting reaction between 5-norbornene-2,3-carboxylic anhydride and a silicon hydride in the presence of a platinum catalyst. As taught by Ryang, anhydride terminated polydiorganosiloxane was made by equilibrating the 1,3-bis(norbornane-dicarboxylic anhydride)tetraorganodisiloxane with cyclopolydiorganosiloxane in the presence of an organic solvent such as toluene and an equilibration catalyst such as sulfuric acid. Although valuable results have been achieved by Ryang in accordance with the aforementioned equilibration procedure, experience has shown that when equilibration is conducted in the presence of an organic solvent, a significant amount of cyclopolydiorganosiloxane is generated, which can be up to 99% by weight of the initial diorganosiloxane utilized mixture. It would be desirable to make norbornane anhydride substituted organosiloxane utilizing norbornane-dicarboxylic anhydride siloxane along with cyclopolydiorganosiloxane or organo terminated polydiorganosiloxane or mixtures thereof to produce norbornane anhydride substituted organosiloxane without the generation of a significant amount of cyclopolydiorganosiloxane.
As taught in copending application Ser. No. 793,360, filed Oct. 31, 1985, for Buese, now U.S. Pat. No. 4,598,135 assigned to the same assignee as the present invention and incorporated herein by reference, improved equilibration results can be achieved by conducting the equilibration of norbornane anhydride substituted organosiloxane with cyclopolydiorganosiloxane or organo terminated polydiorganosiloxane or mixtures thereof under neat conditions in the presence of an equilibration catalyst, such as trifluoromethane sulfonic acid. Although improved results are obtained with respect to a substantial reduction in the formation of cyclopolydiorganosiloxane in the recovery of improved yields of norbornane anhydride substituted organosiloxane, the resulting equilibration mixture has to be quenched with a quenching agent, such as magnesium oxide, which must be filtered from the equilibration mixture.
It would be desirable to achieve improved equilibration results with respect to the generation of norbornane anhydride substituted organosiloxane, while eliminating the need for a quenching agent requiring a separate filtration step to remove the quenching agent from the mixture.
The present invention is based on our discovery that certain organosilazanes as defined hereinafter have been found useful as quenching agents for acidic norbornane anhydride organosiloxane equilibration catalysts. In addition, it has been found that such organosilazanes can be readily stripped from the equilibration mixture during the devolitization step after equilibration has been achieved.